Igniting device fob combustion



Aug. 24, 1948. LUBBOCK ETAL 2,447,758

v IENITING DEVICE FOR lcomarusron CHAMBERS Fiied Nov. 6. 1942 2sheets-sheet 1 HHH ug- 24,1948. l. LUBBOCK ErAl. 2,447,758

IGNITING DEVICE FOR COMBUSTION CHAMBERS Filed Nov. 6. 1942 2Sheets-Sheet 2 IGNITION FLAME .K

INVENToRs (4040 www Aitor/ceq Aug. 24,

UNK l 2,447,758 IGNITING DEVICE Fgg'sCOfBUSTION lz. l;

Isaac Lubbock and Harold James Poole, London,

England;

said Lubbock ossilnor to The Asiatic Petroleum Company, Limited, London,England Application November 8, 1942, Serial No. 484,833

ln Great Britain November 7, 1941 This invention relates to improvementsin ignition devices for combustion chambers in which reactingsubstances, e. g. Ia liquid fuel and a liquid oxidant such as liquidoxygen, are fed so as to burn under pressure, the products of combustionbeing discharged to an engine or to -a reaction nozzle or the like.

'Ihe object of the invention is to provide a chemical igniter which canbe caused to operate practically instantaneously 'and in which theigniting substance, so far as its rate of burning is concerned, will notbe seriously influenced by the pressure produced in the combustionchamber. A further object is to ensure that the igniter housing will notbe damaged by the subsequent high temperature produced in the combustionchamber.

According to the invention, a hollow igniter body of metal is employedwhich may be in the form of a. bulb screwed. bolted or otherwiseconnected to the combustion chamber wall and having a nozzle registeringwith an oriilce leading to the combustion chamber. Within this body orbulb is accommodated a charge of cordite or similar propellant havingthe characteristics of burning at an increasing rate with pressure, thischarge being ignited inthe conventional manner by means of a primer ofpowder, fine pellets or strips of the propellant itself. 'I'he firing ofthe charge is preferably carried out electrically by any of the wellknown types of electrical fuses or by percussion or friction cap.

The nozzle leading to the combustion chamber is of a size and shapewhich coupled with the known characteristics of the cordite orpropellant charges creates a pressure within the igniter body not lessthan twice the maximum pressure reached in the combustion chamber uponignition of the reacting substances. In this way, fromI the well knownlaw of discharge of nozzles against pressures below the critical one ofapproximately half the higher pressure. the reaction on the rate ofburning of the igniterV will be negligible. In

other words, by so designing the nozzle leading from the igniter to thecombustion chamber .that 'the'pressure inside the ign-iter is always atleast twice the pressure existing in .the combustion chamber, the rateof discharge of gas from the igniter through the nozzle remains constantand the pressure in the combustion chamber has no effect upon therate ofburning of the igniter charge and .the pressure produced thereby.

The nozzle may be followed by a somewhat enlarged straight orapproximately straight orice in the combustion chamber wall as opposedto an expanding iet so as to create friction and reduce the gas velocitybelow the maximum obtainable on expansion of the lgni-tlng gases .thussecuring as high an ignition temperatureas possible.

'I'he metal body of the lgniter may be lined with an insulating materialwhich may be of any o! the well known refractory types includinggraphite, but the lining would not be ud where the .time of operation ofthe combustion chamber is less than that which would give excessivetemperatures Within the igniter casing.

The nozzle described above may be made of metal or refractory material,the latter being used lto prevent overheating both during the ignitionperiod and subsequently. A metal inner -tube may be used within anyrefractory lining to relieve the lining of excessive pressure stresses.

The invention is illustrated by way of example in the accompanyingdrawing wherein Fig. 1 is a sectional elevation of the ignition device,and Fig. 2 is a somewhat diagrammatic view, partially in section,showing -the ignilter of the present invention ln combination with thecombustion chamber of a rocket of known type.

The igniter body which is of metal is shown at i. It is lined withinsulation 2 inside of winch is a metal inner tube 3.

The igniter accommodates a charge of cordite I and the head of theignlter carries a primer 5, above which is the electrical ring meansindicated generally at t.

The block of refractory material I in the bottom of the igni'ter isshaped to form the nozzle 8 having a throat followed by an expandingportion,

as shown.

The ignlter is screwed into the wall 9 of a combustion chamber Il inwhich a liquid fuel and a liquid oxidant, supplied by a suitable burneri2, are to be burned under pressure.

The nozzle 8 of the igniter is ci' a size and shape which coupled withthe known characteristics of the cordite Ycharge creates a pressurewithin the igniter body not less than twice the maximum pressure reachedin lthe combustion chamber upon ignition of the reacting substances.

A straight orifice l0 in the wall 9 of the combustion chamber, whichreceives the gases issuing from the nozzle 8 and leads them to thecombustion chamber, creates friction and reduces the gas velocity belowthe maximum obtainable on expansion of the igniting gases, thus securinga high ignition temperature.

What we claim is:

1. An ignition device adapted to be secured externally to a combustionchamber in which reactingsubstansareiedsoastoburnimderpres sure and thewall of which has an orince, said device having a body constructedinternally to form a space communicating with a nozzle which contractsto a thmat and then merges into an expanding portion. said expandingportion oi the nozzle having its outlet in registry with said oritice, acharge of propellant within said space behind-the nozzle throat, thepropellant having the characteristics of burning at an increasing ratewith pressure. and means for ring said propellant charge. the sine andshape of said nozzle throat being so designed that the propellant whenignited will create a pressure'withln said body not less thansubstantially .twice the maximum pressure reached in the combustionchamber upon ignition of the reacting substances.

2. An ignition device adapted to be secured externally to a combustionchamber in which reacting substances are fed so as to burn underpressure and .the wall oi' which has an oriiice, said device having abody constructed internally to form a space communicating with a nozzlewhich' contracts to a throat and then merges into an expanding portion,said expanding pox-tion of the nozzle having its outlet in registry withsaid oriiice and said oriilce forming a substantially cylindricalcontinuation of the nomle having a diameter substantially the same asthat oi the outlet end o! the nome. a charge oi propellant within saidspace behind the nomic throat. the propellant having the characteristicsof burning at an increasing rate with pressure. a primer. and means forilring said propellant charge, the size and shape oi' said noczlelthroat being so designed that .the propellant when ignited will createa pressurev within said body not less than substantially twice themaximum pressure reached in the combustion chamber upon ignition of thereacting substances.

ISAAC LUBBOCK. HAROLD JAMES POOLE.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS

